| Issue |
120361
|
| Summary |
[InstCombine] `samesign` should be dropped when folding logical and of icmps
|
| Labels |
miscompilation,
llvm:instcombine
|
| Assignees |
dtcxzyw
|
| Reporter |
dtcxzyw
|
Reproducer: https://alive2.llvm.org/ce/z/YSW_NC
```
define i1 @src(i8 %0, i8 %1) {
start:
%2 = icmp samesign eq i8 %0, -1
%3 = icmp ne i8 %0, 0
%4 = icmp ugt i8 %0, %0
%result = select i1 %3, i1 %2, i1 %4
ret i1 %result
}
define i1 @tgt(i8 %0, i8 %1) {
start:
%2 = icmp samesign eq i8 %0, -1
ret i1 %2
}
```
```
----------------------------------------
define i1 @src(i8 %#0, i8 %#1) {
start:
%#2 = icmp samesign eq i8 %#0, 255
%#3 = icmp ne i8 %#0, 0
%#4 = icmp ugt i8 %#0, %#0
%result = select i1 %#3, i1 %#2, i1 %#4
ret i1 %result
}
=>
define i1 @tgt(i8 %#0, i8 %#1) {
start:
%#2 = icmp samesign eq i8 %#0, 255
ret i1 %#2
}
Transformation doesn't verify!
ERROR: Target is more poisonous than source
Example:
i8 %#0 = #x00 (0)
i8 %#1 = poison
Source:
i1 %#2 = poison
i1 %#3 = #x0 (0)
i1 %#4 = #x0 (0)
i1 %result = #x0 (0)
Target:
i1 %#2 = poison
Source value: #x0 (0)
Target value: poison
```
Reported by https://github.com/dtcxzyw/llvm-mutation-based-fuzz-service/issues/14 while reviewing https://github.com/llvm/llvm-project/pull/120177.
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